1. Technical Field of the Invention
The present invention relates generally to an automatic deceleration control system, a vehicle-to-obstacle distance control system, and a system program storage medium, and more particularly to an automatic deceleration control system designed to determine a difference between a target deceleration and an actual deceleration during braking to regulate the braking fluid pressure acting on wheels so that the actual deceleration follows up the target deceleration, a vehicle-to-obstacle distance control system designed to control the speed of the vehicle to bring the distance to an obstacle in front of the vehicle into agreement with a target value, and a storage medium in which a system program of the automatic deceleration control system or the vehicle-to-obstacle distance control system is stored.
2. Background of Related Art
An automatic braking system for automotive vehicles is known in the art which is designed to monitor the distance between a controlled vehicle and an obstacle present ahead of the controlled vehicle and a relative speed to the obstacle using optical techniques or ultrasonic waves to determine the possibility of collision with the obstacle and to turn on a brake actuator if the possibility of collision shows a high level to brake each wheel so as to keep the distance to the obstacle constant for avoiding an accidental collision.
The automatic braking system includes a deceleration detector which detects an actual deceleration of the controlled vehicle and a correcting circuit which determines a difference between the actual deceleration and a target deceleration and corrects a control signal outputted to the brake actuator based on the difference. This system does not always bring the actual deceleration of the controlled vehicle into exact coincidence with the target deceleration and has a dead band within which the pressure regulation of brake oil through the brake actuator is arrested when the difference between the actual deceleration and the target deceleration falls within a given range. The brake actuator includes pressure-rising and pressure-reducing valves each of which is turned on and off in preselected duty cycles to increase or decrease the pressure of the brake oil in stepwise fashion.
Japanese Patent First Publication No. 5-310108 teaches an automatic braking system of the type, as discussed above, which is also designed to alleviate the problem that vibrations occur near a target deceleration by narrowing a brake control dead band. This conventional system, however, has the drawback in that when it is required to change a target acceleration or deceleration moderately, that is, when a difference between the target acceleration or deceleration and an actual acceleration or deceleration is small, a duty factor of a control signal outputted to a brake actuator is so set as to increase the pressure of brake oil slowly, thereby resulting in a time delay between output of the control signal to the brake actuator and a time when the vehicle is decelerated actually.